When eating cold food or hot food, sweet food or acidulous food, a severe electrifying pain of teeth is believed to be caused by stimulating the dentinal nerves of teeth. The dentin of teeth is penetrated by many dentinal tubules, and the inside of the dentinal tubules is filled with tissue fluid. The pain of teeth is believed to be caused, when the dentin is exposed, by stimulation of sensory nerves existing near the boundary between the dental pulp and the dentin induced by forced movement of tissue fluid in dentinal tubules upon receipt of an external stimulus. This stimulus is caused by anything that makes tissue fluid in a dentinal tubule move, and thus a mechanical or thermal stimulus and a stimulus including sweetness, acidity or that causes change in osmotic pressure cause a pain of the dentin. Therefore, a pain is induced by eating or drinking, brushing with a tooth brush, or exercise and hinders daily life severely. Dentinal hyperesthesia includes cervical hyperesthesia following tooth wear caused by improper brushing with a tooth brush or a defect on enamel or cement caused by tooth caries or the like, and hyperesthesia of a root surface caused by gingival recession or the like induced by wrong brushing. Due to recent aging of the population or recent increasing movement to preserve vital teeth, dentinal hyperesthesia caused by gingival recession or tooth root exposure tends to increase.
Many of the remedies currently applied to dentine hyperesthesia aim to arrest the movement of tissue fluid in dentinal tubules. Examples of methods for blocking external stimuli by various materials include (1) a method of mechanically covering an exposed dentin surface with a resin material or glass ionomer cement, (2) a method of sealing tubules with a product capable of reacting with calcium in the dentin using oxalic acid, and (3) a method of sealing tubules by clotting protein contained in tubules with glutaraldehyde.
However, the above-mentioned prior techniques are problematic in that the techniques do not allow reliable treatment for subgingival parts or interdental gaps because of low pH or high toxicity of materials. Moreover, there is a problem that dentinal tubule sealing is not maintained well in oral environments and the effect does not last. In order to solve these problems, the following techniques using calcium phosphate have recently been disclosed.
Patent Document 1 discloses a composition for hyperesthesia capable of preventing or treating dentinal hyperesthesia by use of particles of hydroxyapatite or tricalcium phosphate having a particle diameter of 1.0 μm to 5.0 μm. However, the composition is problematic in that dentinal tubules cannot be sealed densely thereby and durable dentinal tubule sealing cannot be obtained therefrom because calcium phosphate having a particle diameter of 1.0 μm to 5.0 μm unfavorably forms gaps between particles immediately after physically entering into dentinal tubules having a diameter of 2 to 3 μm.
Patent Document 2 discloses a dentinal tubule sealant containing calcium phosphate particles as small as 900 nm or less. According to this document, calcium phosphate particles filled in dentinal tubules function as a nucleus after being surely filled into the dentinal tubules, and can accelerate remineralization. However, mere use of calcium phosphate particles as small as 900 nm or less allows dissolution of the particles having a large specific surface area rather than calcification in oral environments, and it is problematic in that initial physical sealing is not achieved certainly and the sealing is removed by a physical stimulus such as gargling, or eating and drinking.
Patent Document 3 discloses a two-component type dentinal tubule sealant obtained by mixing a material formed of tetracalcium phosphate particles and an alkali metal salt of phosphoric acid with a material containing water to convert them into hydroxyapatite. This sealant allows hydroxyapatite to deposit even at deep parts of dentinal tubules and can seal dentinal tubules densely, but there remains room for reducing the labor in extemporaneous preparation by an operator or improving storage stability when forming a one-component type agent.
Patent Document 4 discloses a two-component dentinal tubule sealant obtained by mixing a material formed of poorly-soluble calcium phosphate particles and a phosphorus-free calcium compound with a material containing water, thereby converting them into hydroxyapatite gradually. This sealant excels in dentinal tubule sealability immediately after treatment and also excels in the durability of dentinal tubule sealing, but there remains room for reducing the labor in extemporaneous preparation by an operator or improving storage stability when forming a one-component type agent.
As disclosed in the above-cited patent documents, the disclosed products are insufficient in initial dentinal tubule sealability or are problematic in the durability of dentinal tubule sealing or require extemporaneous preparation or have room for improving storage stability when forming a one-component type agent.